Refractory body for electrical apparatus



Nov. 27, 1956 A. LATOUR REFRACTORY BODY FOR ELECTRICAL APPARATUS FiledMarch 8, 1952 Inventor Andr LATOUR B, Kwk MMM United States PatentREFRACTORY BODY FOR ELECTRICAL APPARATUS Andr Latour, Grenoble, France,assignor to Etablissemerits Merlin & Gerin, Socit Anonyme, Grenoble,France, a corporation of France Application March 8, 1952, Serial No.275,639

Claims priority, application Belgium March 28, 1951 4 Claims. (Cl.200-144) The invention is concerned with the protection of electricalapparatus at those places where they are exposed to the action ofelectrical arcs.

More particularly the invention is concerned with insulating, refractorybodies and methods of making the same for use as, or for presenting,faces whereupon in electrical apparatus an arc plays or which otherwiseare exposed to the action of such an arc.

The invention thus refers to electrical apparatus such as circuitbreakers or switches or other apparatus where there are provided piecesor facings of insulating, refractory material for the purpose ofconfining the arc to a predetermined path.

An object of the invention thus is the improvement of the quality,durability or other characteristics, of such pieces or facings which, ofWhatever type or for whatever purpose they may be, blow cheeks orflanges, partitions, deflecting walls or barriers, bafiles, arcchambers, or the like arcing plates, are, an indefinite number of times,in more or less close contact with the electrical arcs while the arcsare conveyed on a predetermined path along the faces of these arcingplates and develop and expand until extinction. The invention thus isconcerned with arcing plates where, an indefinite number of times andduring short periods of time or transitorily, the faces of these arcingplates are exposed to the action of the arc are heated with extremerapidity and intensity and then allowed to cool down.

The invention thus has for its object the extention of the lifetime ofsuch apparatus by removing the causes or possibilities of local fusings,followed by sealing or flaking of the material or the fissuring thereofor its allotropic transformation or deterioration owing to the rapidlyalternating expansion and contraction of the material under the actionof the arc.

Furthermore it is the object of the invention to improve the functioningof the apparatus by obviating the causes which otherwise, under theaction of an arc of high intensity, would render such faces ofinsulating, refractory material conductive and wouldthus retard theextinction of the arc, or would volatilize superficial portions of thematerial and thus release vapours whose counter-pressure would impedethe desired development of the arc.

In order to achieve these and other objects, the invention contemplatesthe making of the pieces of facings on which the arc plays or whichotherwise are exposed to the action of the are as bodies in whichinsulating, refractory material is employed in its purest condition andwhich are formed as a briquette of a particular physical structure.

In accordance with the invention the insulating pieces or their facings,or the bodies used as, or presenting, faces exposed in electricalapparatus to the "action of electrical arcs, in contrast with suchbodies of the conventional type, are no longer homogeneous but arecomposed of grains of insulating, refractory material, con- PatentedNov. 27, 1956 tiguous grains being bound together at their contactingedges or surface areas and with voids left at and between thenon-contacting surface areas of the grains.

This binding together of contiguous grains is made by briquetting inparticular by fritting the grains together at contacting edges orsurface areas, areas which are very small relatively to the total orproper surfaces of the grains.

The term flitting as employed in this specification and in the claims isto be understood as a vitrifying process under such conditions oftemperature and pressure that the grains are only imperfectly vitrifiedso as to fuse only superficially and particularly only to such an extentthat contiguous or neighboring grains fuse together at the smallcontacting edges or areas without the grains or the individual grainsbeing fused down as a whole.

The fritting process may be carried out without or with the aid of abinding or fluxing agent.

The grains which are thus subjected only imperfectly to this frittingprocess preserve fully their valuable characteristics such as theirresistibility against thermal and electrical stresses.

It is thus possible to employ in electrical apparatus for the faces onwhich an arc plays, or which otherwise are subjected to the action of anare, a body composed of grains of insulating, refractory material inpurest condition, the grains being bound together at surface areas smallrelatively to the total or proper surfaces of the grains but beingotherwise separated by voids, so that the whole surface exhibits in anydirection a succession of alternating grains and voids.

For the purposes of the invention any appropriate refractory material,natural or artificial, may be employed, such as quartz, smelted silica,corundum, zirconia, glucina, magnesia, or the like, now-argillousmaterials. A preferred form of carrying out the invention will be theutilization of such refractory material in pure condition, particularlyin the form of electro-cast refractories or more specificallyelectro-cast magnesia, all of which refractories may be brought intoproper grain or particle size by grinding, crushing, or otherwise.

In the accompanying drawing which forms part of this specification andis to be understood explicative of the invention but not limitative ofits scope, I have illustrated diagrammatically on an exaggeratedenlarged scale a portion of an insulating, refractory body of theinvention.

The grains of insulating, refractory material are designated by 11.Contiguous or neighboring grains are, as indicated at 12, bound togetherat contacting edges or surface areas small in size relatively to theproper or total surfaces of the grains. Voids, indicated at 13, are thusleft between the individual grains 11. 14 represents a face of the bodyto be exposed to the action of an electric arc. On this face, grains andvoids thus alternate, the face thus having an aspect similar to that ofthe surface of an abrasive.

A surface of grains interspaced by voids, formed in accordance with theinvention, withstands advantageously the strains of an electric arc.Should even the out- Ward faces of the grains start to volatilize, thelateral and inward faces of the grains would not be affected sinceobviously these faces are less exposed to the arc and consequently arenot liable to volatilize. In any case, the voids cannot contribute tothe generation of vapor and it has been established that for a givenrefractory body and under equal other conditions a dis continuoussurface produces less vapor than a continuous surface.

Moreover, the numerous cavities or voids left between the grainsconstitute as many condensation chambers capable of absorbing andcondensing the vapor released by the thermal action of the are. For thesame reason, the counter-pressure developed by the vapor will bereduced.

The discontinuity of the surface presents another actvantage. Throughthis discontinuity, the increase in superficial conductivity at theextremely high temperature of the arc, or, in other words, the decreasein superficial insulating power which might result from this veryconsiderable raise of the temperature, is less noticeable. in fact, theline along which the arc moves and vanished on the surface presentsitself as'a zigzag line, a line thus which under otherwise equalconditions is longer than the line would be on a smooth and continuoussurface.

Finally, the section of the passage offered to the leakage current islikewise greatly reduced through the presence of these cavities or voidsand also owing to the fact that the grains are in contact with oneanother only at surface areas of very small dimensions.

The size of the grains may vary within wide limits. Practically, goodresults are obtained with grain sizes so small that the grains pass 0.59to 0.074 mm. sieve openings, corresponding to sieves Nos. 30 to 200, U.S. Standard.

In a preferred embodiment of the method of the invention, the grains arebound together simply by fritting, a process analogous to autogenouswelding By means of this method the refractory body may be producedunder full preservation of its purity.

Whereas this fritting process, ever according to the specific materialemployed, will require higher baking temperatures, lower, moderatebaking temperatures will sufiice, for instance ofthe order of 1000 C.,if the grains at their contacting areas are cemented together with theaid of very small quantities of a fiuxing agent whose adhesiveness maybeactivated or realized already at such moderate temperature.

Such fiuxing agent, well known in the art, may be constituted byaluminous, magnesic, calcic, or alkaline silicates or analogous boratesor any other more or less vitrifiable agent and are employed for thepurpose of combining with the siliceous material of the grains bysuperficial attack or reaction and of thus yielding a vitrified surfacelayerglass, enamelwhich thus binds the grains together.

Water or an organic binder may be employed, as also conventional in theart, for holding the grains together in the preliminary stage of theprocess. Whichever the composition of such fiuxing or binding agent maybe, it should be employed in a proportion sufiiciently small so as forthe voids left between the grains not to be filled up by the fiuxing orbinding agent.

For the purpose of exemplification only, it may be indicated that asatisfactory product for the purposes of the invention may be obtainedby employing a composition which contains a few percent of a fiuxingagent of the aforesaid vitrifiable or vitrifying type, 10 percent ofkaolin, the remainder being constituted by grains of periclase of a sizeto pass 0.125 mm. sieve openings, corresponding to sieve No. 120, U. S.Standard. A conventional cold binder, such as water or an organicbinder, is admixed with this composition, the mass brought into a moldand therein subjected to a pressure of several hundreds of kilograms persquare centimeter at a temperature of about 1000 C. and the grains thusbound together at the contacting edges or surface areas.

I claim:

1. Arcing plates for circuit breakers, switches and the like electricalapparatus comprising a porous refractory body consisting essentially ofgrains of a refractory insulating substance bonded together byautogenous fritting only at the contacting areas of their surfaces toleave a substantial portion of voids between said grains.

2. Arcing plates as defined in claim 1 wherein said grains are bondedtogether at the contacting surface areas thereof by autogenous frittingin the presence of a fluxing agent.

3. Arcing plates as defined in claim 1 wherein the said grains areselected from the group consisting of quartz, smelted silica, corundum,zirconia, glucina and magnesia.

4. Arcing plates as defined in claim 3 wherein said grains consist of afused refractory selected from the defined group.

References Cited in the file of this patent UNITED STATES PATENTS883,366 White Mar. 31, 1908 1,014,098 Sachs Jan. 9, 1912 1,016,443 SachsFeb. 6, 1912 1,713,580 Williams May 21, 1929 1,812,376 Ross et a1. June30, 1931 2,119,400 'Nowak May 31, 1938 2,165,819 Albers-Schonberg July11, 1939 2,200,125 Slepian May 7, 1940 2,206,557 Bennett July 2, 19402,223,959 Lohausen Dec. 3, 1940 2,529,566 Monack Nov. 14, 1950 FOREIGNPATENTS 68,409 Germany 1893 98,591 Sweden 1940 385,328 Great Britain1932 591,551 Great Britain Aug. 21, 1947

